Heretofore smart cards used a housing similar to old plastic cards, including a microcomputer and battery. Contact with the card reader was through ohmic contacts on the card's surface. However, such prior devices are not in large scale use, because of several problems.
The packaging problem--using a flexible package, like a plastic credit card, results in damage to electronic components inside. A rigid package, on the other hand, is subject to tremendous forces in the pocket or wallet, so it can break. The package has to be hermetically sealed, to protect the electronic parts. But then it is difficult to replace the battery.
Danger of theft--it is well known that the cards attract thieves, cards can be lost. Therefore it is desirable to be able to secure or conceal the card.
The connection to the card reader problem--until now electrical contacts on card's surface were used to transfer information. This method is not reliable, because of dirt or mechanical damage.
The conventional identification device contains a key which is present and readable all the time, while energy is supplied to the device; the key is in the form of a specific shape of a specific resonating frequency or a transmitted code. Unauthorized parties can learn the key and misuse it. The user has manual control over the transmitted code, and selects the code to be transmitted.
Portable random access memory devices known in the art allow the user full access to and control over the stored data. The data transfer and storage is controlled manually. This structure cannot be used in smart cards, because of the sensitivity of the stored data--the user must not be allowed to change the data detailing the approved credit limit, the history of money withdrawals, the number of tickets he/she is entitled to, or the identification code.
A display to the user is needed in addition to the electrical connection to the outside world. There are practical difficulties in adding a display to existing smart cards.
There exists time dependent information, like a credit card limited to a certain period, or delayed payments--therefore a link to a time measuring device is needed.